1. Field of the Invention
The present invention relates to a lead-rotatable mechanical pencil in which the front end of a lead worn away by writing can be rotated without changing the user's gripped position of the mechanical pencil.
2. Background Information
When the front end of a lead is worn away by writing, the line becomes thicker, and therefore there has been known a mechanical pencil having a lead-rotating mechanism in which a pointed lead condition can be recovered by rotating the lead. As the lead-rotating mechanism, various structures have been known.
For example, in a mechanism utilizing writing pressure described in Japanese Patent No. 4240417, a front end of a slider protrudes from a tip member disposed at the front end of a barrel and retracts at the time of writing, and this retraction movement makes the lead rotate via a gear. However, in this mechanism, the lead rotates freely by the presence or absence of the writing pressure regardless of the wearing condition of the lead. For example, when a figure made of straight lines is continuously drawn, even if the lead is not worn away, the lead rotates when the front end of the lead is raised apart from paper face. In such instance, when the writing front end is raised in writing, the thickness of straight line is changed halfway. When characters are drawn, since the lead rotates per stroke of the character, it is difficult to keep the thickness of the line uniform. As explained above, in such a structure in which the lead is made to rotate on the basis of writing pressure, the front end of the lead may undesirably rotate regardless of the user's intention. In addition, this type mechanism uses a mechanism that rotates the gear with the movement on writing, and the front end of the slider may sometimes slip into the inside of a tip member, and therefore this mechanism is hardly usable.
With respect to a side knocking type-mechanical pencil, a mechanism in which a lead is rotated by pressing a side knocking button has been known. For example, in the mechanism of a mechanical pencil described in Japanese Patent No. 3852172, a slider is moved by pressing a knocking piece, the movement of the slider moves a lead reservoir, the movement of the lead reservoir moves a slide cam, and the movement of the slide cam moves a rotating cam. The rotation of the rotating cam turns the lead reservoir and a chuck member fixed to the lead reservoir.
As mentioned above, conventionally known lead rotating-type mechanical pencils have complicated structures, a large number of parts, and such pencils cannot be produced and assembled at low cost.